Why do cliff swallows form nesting colonies?

Cliff swallows (Hirundo pyrrhonota) form nesting colonies primarily to facilitate information sharing regarding food resources. Because these birds rely on highly variable insect populations, colonial living allows unsuccessful foragers to observe and follow successful individuals back to productive feeding sites.1

Once these colonies are established, additional benefits emerge, such as more efficient detection of predators. However, this social structure also carries significant costs, including an increased susceptibility to ectoparasites like fleas and ticks, a higher incidence of food stealing known as kleptoparasitism, and the necessity of traveling further to reach foraging areas.1

The decision to nest in groups represents a delicate evolutionary balance between these competing costs and benefits, resulting in a wide range of colony sizes.1